1. Field of the Invention
Exemplary embodiments of the present invention generally relate to an image forming apparatus such as an electrophotographic copier, facsimile machine, printer, plotter, multifunctional machine, or printing machine, and an image forming method. In particular, exemplary embodiments of the present invention relate to an image forming apparatus and method using a cleaning blade as a cleaning device which cleans residual toner remaining on an image carrier.
2. Discussion of the Background Arts
Generally, in an image forming apparatus using an electrostatic photography process, an electrostatic latent image corresponding to the image of a document is formed on a surface of a rotary photoconductor previously charged to a predetermined polarity and serving as an image carrier. The electrostatic latent image is developed by a development unit provided at a predetermined position around the photoconductor. That is, with fine powder toner charged and supplied from the development unit, the electrostatic latent image is developed into a visible image. As the photoconductor rotates, the toner image formed on the photoconductor reaches a transfer unit to be transferred to a sheet-like medium, i.e., a so-called transfer material (hereinafter referred to as the recording sheet) conveyed to the transfer unit. Thereafter, the toner image transferred to the recording sheet is fixed thereon by a fixing device. Further, after the transfer of the toner image to the recording sheet, residual toner remaining on the photoconductor is removed by a cleaning device provided at a predetermined position around the photoconductor.
In an image forming apparatus which removes the toner remaining on the photoconductor by using a cleaning blade, abnormal noise occurs in some cases due to friction between the photoconductor and the cleaning blade (hereinafter referred to as blade squeak). The blade squeak tends to occur particularly when the photoconductor is rotated at a relatively low speed or is about to stop.
In view of the above, according to a background technique, in an image forming apparatus in which a photoconductor having a surface layer formed by a bisphenol Z polycarbonate resin is cleaned by a cleaning blade formed by a polyurethane rubber, each of characteristic values of the cleaning blade is specified in a certain range to prevent the blade squeak. Specifically, the background technique specifies the hardness of the cleaning blade in a range of from 60 degrees to 80 degrees, and the rebound resilience of the cleaning blade in a range of from 10% to 65%. Further, the background technique specifies the absolute value of the charge amount of the residual toner as in a range of from 5 μC/g (micro Coulomb per gram) to 50 μC/g. With some types of toner, however, it is difficult to prevent the blade squeak. It is also difficult to prevent the blade squeak when the photoconductor is rotated at a relatively low speed.
To prevent such inconvenience, another background technique specifies the characteristic values of the cleaning blade and the absolute value of the charge amount of the residual toner to prevent the blade squeak. Further, this background technique provides a weight inside the photoconductor, and specifies a particular weight ratio between the photoconductor and the weight to prevent the blade squeak.
In an attempt to prevent the blade squeak by regulating the characteristic values of the cleaning blade, as in the first type of background technique, the blade squeak may still occur due to variation in the characteristic values of the cleaning blade. Further, cleaning failure may occur because the characteristic values are unsuitable for attaining the required level of cleaning performance. Further still, the incidence of abnormal noise tending to occur in a relatively low temperature environment (hereinafter referred to as blade chatter) may increase.
Meanwhile, the second background technique described above can prevent the blade squeak due to the friction between the photoconductor and the cleaning blade and the abnormal noise such as blade chatter. Further, the second background technique is advantageous in that, for example, the blade characteristic values can be set to be suitable for attaining the required cleaning performance. However, the provision of the extra weight inside the photoconductor undesirably increases the costs. Further, the weight may be misaligned depending on how the weight is installed, resulting in a variety of troubles.